This invention relates to the treatment of the surfaces of aluminum and its alloys for cleamning and/or etching purposes. After such treatment, such surfaces may be subjected to further processing such as the formation of a chemical conversion coating or anodic treatment or the like.
It is known to use aqueous alkali solutions to clean and/or etch the sufaces of aluminum and its alloys. In many cases, however, such etching of the aluminum surfaces produces an undesirable precipitate in the solutions. The precipitate tends to mar the aluminum surface and interfere with processing treatments thereafter. Various attempts have been made to overcome this problem such as with the inclusion of gluconates or tartrates in the solutions, including those containing tertiary amino-alcohols and solvents. Such procedure have met with limited success.
Another problem is that the etch rate is customarily too fast which results in a large consumption of the etchant as the etched aluminum surface cannot be isolated from the etch bath rapidly.
The etchant and etching method of this invention provides a relatively inexpensive etchant that has a relatively low consumption rate when compared to other systems. Such lowered etchant rate produces an appreciable reduction in the consumptin of the etchant.
A typical etchant of the prior art is that such as described in British Patent Specification No. 1,160,945 published Aug. 6, 1969, by Amchem Products, Inc. It is thus seen with the British patent specification disclosure that the etchant concentrate there includes an alkali hydroxide, the gluconate ion, ethylene glycol or a derivative thereof and an ethanol amine or a derivative thereof-all in specified proportions to provide a consolute aqueous concentrate.
The etchant of the present invention provides an etchant with a consumption rate similar to that of the etchant of the British patent specification but at a far reduced cost of materials.